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Honeywell Motorised Valves ~ Problems and Fault-finding
Customer reported that hot water would not heat unless the radiator heating was on too.
This system had 2 Honeywell V4043H two-port motorised zone valves, one controlling the radiator circuit and one controlling the hot water circuit. With the central heating programmer set for hot water on (but not central heating) the boiler would not fire to heat the hot water. If central heating was selected too, and the room thermostat turned up so that the radiators came on, the hot water would heat up.
The typical sequence with two-port zone valves works like this: The programmer is set for a hot water demand (hot water on) and sends a signal to the hot water cylinder thermostat. If the cylinder stat is calling for heat it sends the signal on to the zone valve controlling the hot water circuit and this drives the valve open.
Most Honeywell zone valves are closed in the de-energised state. They are fitted with a manual lever, running in a slot on one end of the valve. When the valve is closed, this lever is "loose" for about one third of the travel of the slot with the rest of the travel pushing against a heavy spring. When the valve is powered open the lever is loose for the entire travel of the slot. With hot water selected on the programmer, and the cylinder thermostat calling for heat, we checked the lever and it was loose across the whole travel of the slot but the boiler didn't fire.
Most Honeywell V4043H zone valves are also fitted with an auxiliary circuit, two wires, a grey wire in and an orange wire out, connected by an internal switch or end switch. The grey wire is (normally) permanently Live. When the valve is driven fully open by the signal from the programmer, the internal end switch closes, connecting the grey wire to the orange wire which also becomes Live. The orange wire then sends a signal to operate the boiler and pump.
The hot water zone valve on this customer's system was winding most of the way open but not quite far enough to close the end switch, so it could not fire the boiler. With the valve largely open, hot water would heat up if the other Honeywell zone valve (the heating valve) was firing the boiler but not if hot water alone was selected on the programmer or if the room thermostat was up to temperature.
Sometimes it is possible to free a sticking valve, at least temporarily, by repeatedly driving the valve open manually using the lever (with the system switched off) or by removing the power head (the actuator) and repeatedly operating the valve manually using a small spanner. But be warned! Early Honeywell motorised valves had actuators (powerheads) which could not be removed without draining down first. If you disconnect these, water will flood out. We believe that the valves with powerheads which can be safely removed are the ones with the "pip" on the top of the silver metal case but we are not certain of this. If we come across a very old valve without the pip (and these are usually 20 or more years old) we never remove the powerhead!
If you remove the powerhead and operate the valve mechanism manually using a small spanner, be careful not to turn too far or too hard. The small rectangular brass "tongue" which operates the valve below only turns few a few degrees of arc and you must feel for this. It does not turn full circle like some valves!
We changed the failing zone valve with a new 22mm Honeywell V4043H zone valve and tested the operation. Everything worked normally with the hot water now operating correctly on its own again.
Most domestic Honeywell zone valves are either 22mm compression (V4043H1056) or 28mm compression (V4043H1106) though they are also available as ¾" BSP Female (V4043H1007) and 1" BSP Female (V4043H1080). All four of these valves have an auxiliary switch.
The Honeywell ½" BSP Female zone valve (V4043C1156) does not have an auxiliary switch.
Most Honeywell zone valves are closed in the de-energised state (all of the valves above) but Honeywell also make a 22mm compression zone valve which is open in the de-energised state (V4043B1257) and a 28mm compression zone valve which is open in the de-energised state (V4043B1265). Both these valves are much rarer but it's important to replace with the correct valve.
22mm Honeywell V4043H1056 zone valve showing the "pip" on the top of the silver metal case and the manual lever at the bottom of the valve
Honeywell V4073A mid-position motorised valve (3 port valve)
Customer reported hot water working OK but no central heating.
Since the boiler worked OK for hot water we looked at the programmer to check that it was set to call for heating and checked that the room thermostat was set high enough to be calling for heat.
The manual lever of the 3 port valve was only slack for about one third of the length of the slot which is the normal position for hot water only. The valve spindle did not feel unusual (tight) when we pushed the lever against the spring and the valve returned normally.
Using a multimeter set to 750V ac we checked for 230V between the valve white wire and blue wire (in the local junction box) and found 230V present so we suspected the valve motor.
After isolating the electrical power we disconnected one lead from the motor within the valve actuator and checked the resistance through the motor across the two motor leads. This figure is normally about 2400 ohms but in this case the leads were open circuit, indicating a break in the motor windings.
We changed the motor for a new genuine "Synchron" motor (our experience of cheaper, generic motors is that they can fail very quickly) and the system worked fine, with the mid-position valve opening to heating correctly on demand.
Original Synchron motor removed from the Honeywell V4073A valve. The Synchron motors fitted to Honeywell motorised valves have blue wires. Most Synchron motors have orange wires. The manufacturing date code is written on the side of this motor, 9823, week 23 in 1998.
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Customer reported radiators getting hot whenever hot water was selected and with no heating selected.
Unwanted hot radiators can be caused by bad pipework design but this system had had no pipework changes and had worked normally before. The Honeywell V4073A motorised valve rests in the hot water only position (the heating port, A, is closed) when the valve is de-energised. However, if hot water was satisfied and heating was the last thing calling, the valve can remain partially energised with the heating port open.
We switched off the power and the valve rested in the hot water only position. Typically, in this position, the lever is loose in the slot for about one-third of its travel, with the remaining two-thirds of the travel pushing against a heavy spring. Operating the manual lever, the valve felt normal. Sometimes you can clearly feel that the valve is stiff, indicating that the valve spindle may be seizing up. Repeatedly operating the manual lever for the full length of the slot may temporarily resolve this.
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With the power back on and hot water only selected, the valve rested in the correct position. If it had opened the heating port (and the lever become loose for all, or nearly all, of the travel in the slot) we would have been looking for a fault elsewhere, either a fault with the central heating programmer or the room thermostat or with the wiring.
With the boiler running, the pipe from the motorised valve (port A) to the radiators immediately became hot, indicating a fault in the valve. The rubber ball in the Honeywell valves can become dented if left in the hot water only position for a long period. This often happens during the Summer when no heating is called for. The dent prevents the ball from seating correctly for a while, allowing a small amount of let-by into the radiator system but this will often resolve itself after a few days. Honeywell designed the valve so that the ball turns slightly on its spindle each time it sits down. Clever! When we buy new valves to put on stock we check that they are in the locked open "manual" position for storage. That way the ball doesn't sit down and doesn't dent.
This ball was either permanently damaged or the seating was damaged or contaminated so we changed the complete valve, both the power head (actuator) and the body and the problem resolved, hot water cylinder warming up normally with no unwanted hot radiators.
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The Honeywell motorized valves we see most commonly in the UK are the Honeywell V4043H motorised zone valve (Honeywell 2 port valve) and the Honeywell V4073A mid-position valve (Honeywell 3 port valve). Both motorised valves use the same Synchron valve motor.